How can I do calculations in swift

I'm making a Quadratic Solver. As shown on the picture, I have value a,b,c. I want to use the formula x=(-b+-√(b^2-4ac))/2a to solve it. I would like the result to be shown at x1 and x2. What should I write in the code?

My codes are below

import UIKit

class ViewController: UIViewController {

@IBOutletweakvar a: UITextField!

@IBOutletweakvar b: UITextField!

@IBOutletweakvar c: UITextField!

@IBAction func solve(_ sender: AnyObject) {

equation.text = "\(a.text!) x^2 + \(b.text!) x + \(c.text!) = 0"

x1.text = (-b+(√b^-4ac))/2a

x2.text = (-b-(√b^-4ac))/2a

}

@IBOutlet weak var equation: UILabel!

@IBOutletweakvar x1: UILabel!

@IBOutletweakvar x2: UILabel!

override func viewDidLoad() {

super.viewDidLoad()

// Do any additional setup after loading the view, typically from a nib.

}

override func didReceiveMemoryWarning() {

super.didReceiveMemoryWarning()

// Dispose of any resources that can be recreated.

}

}